if (document.images) {
 firston= new Image(340,200);
 firston.src="../../img/yrlvl/firsthover.png";  
 firstoff= new Image(340,200);
 firstoff.src="../../img/yrlvl/first.png";

 secondoff=new Image(340,200);
 secondoff.src="../../img/yrlvl/second.png";  
 secondon=new Image(340,200);
 secondon.src="../../img/yrlvl/secondhover.png"; 

 thirdoff=new Image(340,200);
 thirdoff.src="../../img/yrlvl/third.png";  
 thirdon=new Image(340,200);
 thirdon.src="../../img/yrlvl/thirdhover.png"; 

 fourthoff=new Image(340,200);
 fourthoff.src="../../img/yrlvl/fourth.png";  
 fourthon=new Image(340,200);
 fourthon.src="../../img/yrlvl/fourthhover.png";
}

function lightup(imgname) {
 if (document.images) {
  document[imgname].src=eval(imgname + "on.src");
 }
}

function turnoff(imgname) {
 if (document.images) {
  document[imgname].src=eval(imgname + "off.src");
 }
}